pending on which
	of X and/or Y are zero, plus tuple of nonzero ones.  If both are zero,
	it returns a single zero still.

	>>> _categorizeVector((0,0))
	('0', (0,))
	>>> _categorizeVector((1,0))
	('h', (1,))
	>>> _categorizeVector((0,2))
	('v', (2,))
	>>> _categorizeVector((1,2))
	('r', (1, 2))
	r